The use of an extruded, solid colored or clear, polyvinyl chloride, round cross-section welding rod is well known in the art to join two pieces of vinyl resilient flooring together. This prior art process uses an unfilled, highly plasticized, colored polyvinyl chloride formulation that is in turn extruded through a round die to form a round cross-section, flexible, easily cut rod for seam sealing.
Extrusion yields a solid color rod or, in some cases in which there are shade variations, a swirl effect such as a barber pole results. In no instance is a distinct sharp edge design obtained. The solid color rod areas appear as a seam of solid contrasting color at every welded installation site creating a discontinuity in the flooring surface. This disrupts the flooring pattern image. The desire for a single image flooring or a flooring surface wider than the width of the flooring product, but having a continuous image has been expressed by many designers, architects, etc. No known welding rod containing a distinct pattern is known. Attempts to make such a patterned welding rod have been made in the United States, Europe, and the Far East, especially Japan, without success.
Attempts to fabricate extruded rods with colored particles requires the use of hard, non-thermoplastic, or solid colored particles that will maintain their image and do not flow during the heat developed during blending and extrusion. However, during extrusion these hard particles score or cut into the extruder barrel causing damage to the equipment. Further, they prevent the smooth, easy cutting or skiving of the welded rod when removing the excess rod material above the wear surface of the flooring, thus yielding a non-smooth surface. Such a non-smooth surface provides places where dirt particles can be trapped leading to dirty, unsightly surface conditions.
The use of the multi-colored, chip- or granule-image vinyl resilient sheet flooring for a welding rod has been attempted many times. Generally, a thin strip of flooring is cut approximately the size of a welding rod, typically 2 to 4 mm wide, and welded in the seam area. Strips having an inorganic filler, such as limestone at 20 to 65 weight percent, rapidly elongate and pull apart in the first few inches of welding due to the extremely high welding gun air temperatures, generally 300.degree. C. (572.degree. F.) to 600.degree. C. (1112.degree. F.).
Attempts to utilize the original multi-colored, vinyl chips, that are used in the flooring production, in a mold/press were unsuccessful in maintaining the chip-image. In order to consolidate these chips, whether filled or unfilled with inorganic material, sufficient heat, above 350.degree. F., is required to ensure thermoplastic flow so that the chips are fused together in a solid, coherent mass. This plastic flow is enough to disrupt the chip-images forming a smeared, blurred image. This is not suitable as a welding material since the image is different from the original flooring material.